As solutes constituting a non-aqueous electrolyte in a non-aqueous electrolyte secondary battery, LiPF6, LiClO4, LiBF4, LiAlCl4, LiSbF6, LiSCN, LiCl, LiAsF6, LiCF3SO3, (CF3SO2)2NLi and the like have been used singly or by mixture. In particular, LiPF6 has typically been used as having favorable conductivity.
LiPF6, however, has very low heat stability, and when a battery fabricated using a non-aqueous electrolyte containing LiPF6 as a solute is stored in the charged state at a high temperature, LiPF6 pyrolytically decomposes to produce hydrogen fluoride (HF), PF5 or the like, exerting an adverse effect on the battery. As a result, problems may arise in a case of applying such a battery to appliances such as notebook computers with high calorific power that the batteries are exposed to a high temperature, leading to a sudden decline in battery performance and to generation of a large amount of gas within the battery.
Accordingly, the present invention is directed at solving such problems as thus described in a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, and provides an excellent non-aqueous electrolyte secondary battery, the deterioration in battery characteristics of which in operation at a high temperature and after storage at a high temperature is suppressed and within which gas is generated in a small amount.